# TypedEmitter (/docs/api/typed-emitter)





`TypedEmitter` is the base class that gives every other class in three-start its event API. [`ThreeContext`](/docs/api/three-context), [`ContextModule`](/docs/api/context-module), and [`Object3DBehaviour`](/docs/api/object3d-behaviour) all extend it.

What it does [#what-it-does]

* Wraps an [`eventemitter3`](https://github.com/primus/eventemitter3) instance internally — the proven small/fast emitter, \~1KB minified.
* **Lazy initialization** — the inner emitter is only allocated on the first `on` / `once`. Classes that extend `TypedEmitter` but never have a subscriber pay only one reference slot per instance.
* **Type-safe events** via the `<T extends EventMap>` generic. Keys become valid `event` arguments, tuple values type the listener payload.
* **Encapsulation by design** — `on` / `off` / `once` are public so anyone can subscribe; `emit` is `protected` so only the owning class fires its own events. No external code can fake an event.

```ts
type HealthEvents = {
  damaged: [amount: number, source: string];
  died: [];
};

class Health extends Object3DBehaviour<HealthEvents> {
  hp = 100;
  hit(damage: number, by: string) {
    this.hp -= damage;
    this.emit("damaged", damage, by);     // ✅ inside the class
    if (this.hp <= 0) this.emit("died");  // ✅
  }
}

const health = getComponent(player, Health)!;
health.on("damaged", (amount, by) => console.log(`-${amount} from ${by}`));
health.emit("damaged", 10, "x");          // ❌ compile error: emit is protected
```

The default for `T` is `{}` — a class without an explicit event map can't legitimately call `on` / `emit` (compile error from `keyof {} = never`). This is the type-level opt-in pattern.

Methods [#methods]